Thickness measuring device for cylindrical tank bottom plate

ABSTRACT

Plural auxiliary carts  18  and  19  are connected to a measuring cart  11  in the width direction thereof which travels on a tank bottom plate  31  through universal joint mechanisms  26  and  27 . Reflection type ultrasonic probes  22, 23  and coating film thickness gauges  24, 25  are provided with the respective auxiliary carts  18  and  19 , and also a rotary encoder  32  which measures a traveling distance of the measuring cart  11  is attached to the measuring cart  11 . Based on the outputs of the ultrasonic probes  22, 23 , the outputs of the coating film thickness gauges  24, 25  and the outputs of the rotary encoder  32 , the actual thickness of the tank bottom plate  31 , that is obtained by subtracting the thickness of the coating film at a specific position of the tank bottom plate  31  measured by the rotary encoder, is measured and stored, and the thickness of every portion of the tank bottom plate  31  is displayed on a screen.

TECHNICAL FIELD

The present invention relates to a plate thickness measuring apparatusfor a bottom plate of a cylindrical tank that measures plate thicknessreduction of a bottom plate of a cylindrical tank such as a fuel tank.

BACKGROUND ART

Up to now, in Japan, a plate thickness measurement of a bottom plate ofa cylindrical tank by ultrasonic waves has been performed according tothe Notification of the Fire and Disaster Management Agency. That is, asfor an annular plate within an inside range of 500 mm from an insideface of a side plate, it is performed at intervals of about 100 mm, forexample, at fixed points designated in a staggered manner, and as forother portions of the annular plate and a bottom plate therein, it isperformed at fixed points specified at intervals of about 1 m. Then, asthe result of the plate thickness measurement of the bottom plate at theabove fixed points, if a problem arises where a decrement of platethickness is detected beyond a reference value, plate thicknessmeasurement is further performed for specified positions at intervals of30 mm, in a range of 300 mm radius with the position as a center byusing ultrasonic waves, and hence the plate thickness reduction of thetank bottom near the problem position is known.

However, the following problems that should be solved exist in theconventional plate thickness measurement of the bottom plate of acylindrical tank.

(1) In the plate thickness measurement of the tank bottom plate usingultrasonic waves, since acoustic velocities in a coating film portionand a steel plate portion differ greatly, if the measurement isperformed from an upper surface of the coating film by using a generalultrasonic thickness gauge, a very large measurement error arises in thedetermination of the thickness of an actual bottom plate, i.e., steelplate thickness. Although a multi-echo type ultrasonic thickness gaugeis developed as a counter-measure for this, if there is backsidecorrosion, it is difficult to correctly determine the state of the steelplate thickness reduction by the corrosion of the tank bottom platesince a multi-echo may not be obtained.

(2) Therefore, on the occasion of measurement of steel plate thickness,a method is adopted in which plate thickness measurement is performedfor only the steel plate portion after removing a coating film portionand a recoat is performed after the measurement, however, there is aproblem in that an idle period of a tank becomes long due to themeasurement and an economical problem that costs of coating film removaland recoat arise in addition to measurement cost.

(3) Furthermore, there is a problem that, if an unusual plate thicknessreduction of the steel plate is not detected by the measurement atspaced fixed points, such as unusual plate thickness reduction isignored even if it actually exists in a portion except the fixed points.It is thus impossible to detect the plate thickness reduction of thesteel plate by local corrosion, and hence it is not possible to graspthe plate thickness reduction of the steel plate covering the whole tankbottom plate.

(4) In addition, there is a problem that plate thickness measurement ofthe tank bottom plate cannot be performed simply and quickly since themeasurement is performed at new fixed points, which are given byperforming subdivision with a fixed point as a center, if an unusualplate thickness reduction is detected in the fixed point.

The present invention aims to provide a plate thickness measuringapparatus for the bottom plate of a cylindrical tank which can determineplate thickness reduction of a steel plate covering the whole tankbottom plate without removing the coating of the tank bottom plate.

DISCLOSURE OF INVENTION

A plate thickness measuring apparatus for a bottom plate of acylindrical tank according to the present invention for attaining theabove object has: a measuring cart which travels on a tank bottom plateto be measured; auxiliary carts which are arranged in the widthdirection of the measuring cart and are attached to the measuring cartthrough universal joint mechanisms; reflection type ultrasonic probeswhich measure the thickness of the tank bottom plate, and coating filmthickness gauges which measure the thickness of a coating film on asurface of the tank bottom plate, both of which are attached in each ofthe auxiliary carts; a rotary encoder which is attached to the measuringcart and measures the traveling distance of the measuring cart; and anoperation and display unit that inputs the outputs of the ultrasonicprobes, the outputs of the coating film thickness gauges, and an outputof the rotary encoder, measures and stores the actual thickness of thetank bottom plate that is obtained by subtracting the thickness of thecoating film at a specific position of the tank bottom plate based onthe outputs of the ultrasonic probes and the outputs of the coating filmthickness gauges. Furthermore, the apparatus specifies the position bythe rotary encoder, displays the relation between the position of thebottom plate and the thickness thereof on a screen and stores it.

In the plate thickness measuring apparatus for the bottom plate of acylindrical tank according to the present invention, it is desirablethat plural reflection type ultrasonic probes are arranged in the widthdirection of the measuring cart so that the plate thickness measurementcan be performed in the whole width direction of the measuring cart,whereby it becomes possible to measure the plate thickness of almost allthe portions of the tank bottom plate by making the measuring carttravel on the tank bottom plate. In this case, it is preferable that theauxiliary carts where the ultrasonic probes are mounted are arranged inplural rows in the traveling direction of the measuring cart, and thatthe auxiliary carts in each row are arranged in a staggered or step-likepattern in a plan view.

In addition, in the plate thickness measuring apparatus for the bottomplate of a cylindrical tank according to the present invention, it ispreferable that the reflection type ultrasonic probe is comprised of adouble crystal probe having a transmitting element and a receivingelement, and that the coating film thickness gauge is comprised of aneddy current type sensor. It is thus possible to measure and evaluate astate of the plate thickness reduction by the local corrosion of thesteel plate over the whole tank bottom plate with high precision withoutremoving the coating of the tank bottom plate.

In the plate thickness measuring apparatus for the bottom plate of acylindrical tank according to the present invention, it is preferablethat an operation handle provided in the measuring cart is detachable,and hence, it is possible to measure the thickness of the tank bottomplate with the measuring cart passing under piping provided above thetank bottom plate. Therefore, even if piping which would be obstructiveto the measurement is in a tank, it is possible to measure the thicknessof the bottom plate by passing thereunder.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of each instrument of a plate thicknessmeasuring apparatus for a bottom plate of a cylindrical tank accordingto an embodiment of the present invention, FIG. 2 is a left side view ofa measuring unit of the plate thickness measuring apparatus for thebottom plate of the cylindrical tank, FIG. 3 is a front view of a frontmeasuring cart of the plate thickness measuring apparatus for the bottomplate of the cylindrical tank, FIG. 4 is a right side view of a frontmeasuring cart of the plate thickness measuring apparatus for the bottomplate of the cylindrical tank, FIG. 5 is a block diagram of a dataprocessing system of a plate thickness measuring apparatus for thebottom plate of the cylindrical tank according to an embodiment of thepresent invention, FIG. 6 is a top view of a plate whose thickness is tobe measured, FIG. 7 is a top view showing a plate dividing state of thebottom plate of the cylindrical tank measured by the plate thicknessmeasuring apparatus for the bottom plate of the cylindrical tank, andFIG. 8 is an explanatory diagram showing a plate thickness of the bottomplate of the cylindrical tank measured by the plate thickness measuringapparatus for the bottom plate of the cylindrical tank.

BEST MODE FOR CARRYING OUT THE INVENTION

As shown in FIGS. 1 to 4, a plate thickness measuring apparatus 10 of abottom plate of a cylindrical tank according to an embodiment of thepresent invention has a measuring unit 12 having a measuring cart 11, anoperation and display unit 13 which processes measurement data from themeasuring unit 12, and a water supply unit 14 which supplies water,which is an example of a coupling medium, to the measuring cart 11.Hereafter, these will be described in detail. The operation and displayunit 13 and the water supply unit 14 are not shown in FIGS. 2 to 4.

As shown in FIGS. 1 to 3, the measuring unit 12 is equipped with themeasuring cart 11 having a front cart 15 and a back cart 16 that arearranged and connected. Plural auxiliary carts 18 and 19 are providedrespectively in the front side and back side of an opening 17 providedin a center of the lower part of the front cart 15. Each of theauxiliary carts 18 and 19 has a frame 20 and free wheels 21 attached inthe front, back, right, and left thereof. In a center section of each ofthe auxiliary carts 18 and 19, as shown in FIG. 4, reflection typeultrasonic probes 22 and 23 are arranged. Coating film thickness gauges24 and 25 are provided in the back of each auxiliary cart 18, and thefront of each auxiliary cart 19, respectively.

Respective auxiliary carts 18 and 19 are attached to the front cart 15through gimbal mechanisms 26 and 27 each of which is a universal jointmechanism, and auxiliary carts 18 and 19 move with the free wheels 21 ofthe auxiliary carts 18 and 19 always in contact with a tank bottomsurface 30 regardless of shaking of the front cart 15 in a verticaldirection. That is, generally, the tank bottom surface 30 does not havea perfect flat surface, but has the undulations, and further, sincethere are welded portions of joints and corroded portions in the bottomplate 31 locally, there is unevenness on the tank bottom surface 30.Respective auxiliary carts 18 and 19 follow unevenness of the tankbottom surface 30, and the ultrasonic probes 22 and 23 attached to thesecan move on the tank bottom surface 30 while always having a fixed gap G(refer to FIG. 3). Reference numeral 28 denotes the front, back, right,and left wheels of the front cart 15.

Although the auxiliary carts 18, arranged in the front of the opening17, and the auxiliary carts 19, arranged in the rear of the opening 17,are arranged in the width direction of the measuring cart 11 at the sameintervals respectively, the auxiliary carts 19 in the back row arearranged with shifting by a half pitch (in FIG. 3, X/2) to the auxiliarycarts 18 in the front row. The reason why the auxiliary carts 18 in thefront row and the auxiliary carts 19 in the back row are arranged in astaggered (zigzag) pattern in such a way is as follows.

Although the ultrasonic probes 22 and 23 have a certain width in flawdetection regions, since each is attached to the auxiliary cart 18 or19, owing to the presence of the frame 20 and free wheels 21, anapproach distance L (refer to FIG. 3) between the ultrasonic probes 22and 23 adjacent to each other in a row is inevitably limited. For thisreason, for example, when using only the ultrasonic probes 22 in thefront row (namely, one row), which are arranged in the horizontal singleline, in the auxiliary carts 18, belt-like incapable measurement regionsarise in interzonal portions with the adjacent ultrasonic probes 22. Inorder to be able to measure such belt-like incapable measurementregions, produced by the travel of the auxiliary carts 18, by using theultrasonic probes 23 of the auxiliary carts 19 in the back row (namely,another row), the auxiliary carts 19 are arranged in the centralpositions between respective auxiliary carts 18 in the moving directionof the front cart 15 so that the ultrasonic probes 23 in the other rowcan measure the unmeasurable regions of the ultrasonic probes 22 in theone row.

Although an ultrasonic pulse of each of the ultrasonic probes 22 and 23is emitted from the whole surface of the probe, what can be usedeffectively in measurement is an ultrasonic wave emitted from a portionthe width of which is narrower than this (effective beam width).Therefore, it is necessary to make a pitch X, between centers of each ofthe auxiliary carts 18 and 19 in the width direction, be in the width ofthe adjacent ultrasonic probes 18 and 19 not interfering with each otherand become twice or less than the effective beam width of each of theauxiliary carts 18 and 19.

Here, if the width of the unmeasurable region of the ultrasonic probesin one row is wide, namely, an unmeasurable region has the width of ahalf or more of a attachment pitch of each ultrasonic probe, since allregions cannot be measured even by a group of the ultrasonic probesarranged in two rows, the measurement of all the regions in the widthdirection of the measuring cart 11 becomes possible by providing astep-like group of the ultrasonic probes in three or more rows.

The reflection type ultrasonic probes 22 and 23 used in this embodimentare, for example, split type ultrasonic probes (namely, double crystalprobes) each having a transmitting element and a receiving element,which transmit and receive ultrasonic waves through wedges made ofacrylic resins, polystyrene resins, or the like. It becomes possible toreceive the reflected waves from the lower surface (back face side) ofthe bottom plate 31 without being influenced by the reflected waves ofthe ultrasonic waves from the upper surface (namely, the tank bottomsurface 30) of the bottom plate 31 of the cylindrical tank near totransmitted pulses. Hence, it becomes possible to accurately measure thedistance to a local reduced thickness portion generated in the bottomplate 31.

Eddy current type sensors are used for coating film thickness gauges 24and 25 provided in the auxiliary carts 18 and 19 respectively. If acoating film is on the surface of the tank bottom surface 30, the platethickness measured by the ultrasonic probes 22 and 23 becomes thethickness including the total thickness of the coating thickness andsteel plate thickness. Then, the actual thickness of the coating film ismeasured by the coating film thickness gauges 24 and 25 that arecomprised of the eddy current type sensors, and a more accurate value isobtained by subtracting it from the distance measurements of theultrasonic probes 22 and 23.

A rotary encoder 32 is provided in the front of the front cart 15, whichdetects the rotation speed of the wheels 33 attached to the input shaftof the rotary encoder 32, and the traveling distance of this measuringcart 11 can be electrically measured. A frame 34 to which the rotaryencoder 32 is attached is attached to the front cart 15 in a verticallymovable or freely movable state, and a wheel 33 of the rotary encoder 32always rotates in contact with the tank bottom surface 30.

As shown in FIGS. 2 and 4, at the front and back of the upper portion ofthe front cart 15, a horizontal guide wheel 37 is provided as projectingparts thereof in the right and left sides through supporting tables 35and 36. When the front cart 15 is located near the inside of the tankside plate, this horizontal guide wheel 37 contacts the inside of thetank side plate, and hence the horizontal guide wheel 37 can smoothlymove. Furthermore, the projection length of the horizontal guide wheel37 can be extended up to 275 mm. In front of the supporting table 35, aneyebolt 38 is provided, and hence it is possible to pull this measuringcart 11 with a rope or the like, one end of which is fixed to theeyebolt 38.

Furthermore, as shown in FIGS. 2 to 4, a water distribution unit 39 isprovided in an upper part of the front cart 15, water is supplied to awater spray unit provided in a lower end portion of each of theultrasonic probes 22 and 23 through water feed holes provided in thefront cart 15 via a flexible hose, not shown, which is connected to hosecouplers (nipples) 40 and 41, which are arranged before and after, andgaps between the ultrasonic probes 22 and 23, and the tank bottomsurface 30 are filled with water. Owing to this, while ultrasonic wavesare being sent from the ultrasonic probes 22 and 23 to the bottom plate31, the reflected waves from the bottom plate 31 can also be sent to theultrasonic probes 22 and 23.

The back cart 16 connected with this front cart 15 has a cart frame 44and four wheels 45 provided in the front, rear, right, and left. Ahousing 47 with a lid 46 is provided on this, and a controller 48 of theeddy current sensors constituting the coating film thickness gauges 24and 25 is arranged in this housing 47. With this controller 48, thethickness of the coating film applied on the surface of the tank bottomplate 31 is measured, and is outputted to an operation and display unit13. In addition, although being commonly known, the principle of an eddycurrent sensor is that the thickness of the coating film is detected bypassing an alternating current in a detection coil, detecting that theimpedance of the detection coil becomes small if the distance from theupper surface of the bottom plate 31 thereunder becomes large, andcomparing this with the reference measured beforehand. In addition, itis also possible to arrange an indicator of the controller 48 on the lid46 of the housing 47.

At a far back end of the back cart 16, a removable operation handle 49having the predetermined height (about 60 to 90 cm) is provided, so thatan operator can move this measuring cart 11 in back and forth directionswith this handle 49. In addition, by removing the handle 49, the wholeheight of this measuring cart 11 can be reduced, the measuring cart 11can go under the piping arranged above the tank bottom surface 30, andcan test the tank bottom plate 31. Therefore, it is possible to set theheight H of the measuring cart 11 to be, for example, about 200 mm whenthe handle 49 is removed. Furthermore, to reduce it further, it is alsopossible to set it to be about 100 mm by separating the front cart 15from the back cart 16.

A cable 51, comprised of bundling signal lines of respective ultrasonicprobes 22 and 23, a signal line and a power line for the connection tothe controller 48, a signal line of the rotary encoder 32, and controllines of a measurement start and end switch 50, is provided in a backportion of this back cart 16. This cable 51 is fixed to the back cart 16by a cable stop 52 in the base portion thereof. In addition, the signalof the switch 50 is sent to the operation and display unit 13, and theplate thickness measurement of the tank bottom plate 31 is started andended.

The water supply unit 14 shown in FIG. 1 has a water tank 56 which cancontain sufficient water, a pump 57 which pumps out water from the watertank 56, an electromagnetic valve 58 which turns on and off the waterdischarged from the pump 57. The start and stop of operation of the pump57, and ON/OFF of the electromagnetic valve 58 are performed on thebasis of instructions of a computer 64 by the signal of the measurementstart and end switch 50 provided in the measuring cart 11 being inputtedinto this computer 64 of the operation and display unit 13. A flexiblehose 60 connects this water supply unit 14 with the water distributionunit 39 of the measuring cart 11, and if necessary, water from the watertank 56 is supplied between the ultrasonic probes 22 and 23 and the tankbottom surface 30.

As shown in FIGS. 1 and 5, the operation and display unit 13 has amulti-channel type ultrasonic thickness gauge 63 that sends apredetermined signal to each of the ultrasonic probes 22 and 23 andreceives an output signal from each of the ultrasonic probes 22 and 23,and the computer 64 to which this ultrasonic thickness gauge 63 isconnected through an I/O plate not shown. This ultrasonic thicknessgauge 63, which is a multi-channel type, not only sends pulse signals tothe plurality of ultrasonic probes 22 and 23 connected to this, but alsomeasures plate thickness by receiving the pulse signals which theultrasonic probes 22 and 23 detect, and converts them into a digitalsignal to send it to the computer 64. The coating film thickness gauges24 and 25 are connected to the computer 64 through the controller 48,and the rotary encoder 32 is connected through a counter board 65,respectively. The computer 64 is a personal computer that ismarket-available and comprises a CPU, RAM, ROM, an auxiliary storagedevice, and I/O devices (for example, an A/D converter), calculates theactual plate thickness of the bottom plate 31 by processing signals sentfrom the rotary encoder 32, each of the ultrasonic probes 22 and 23, andeach of the coating film thickness gauges 24 and 25 by the program whichis described below and is set beforehand, and outputs the platethickness with a position thereof to an attached output device (adisplay or a printer).

The system outline of this computer 64 is shown in FIG. 5. A platelayout program 66, a plate thickness display program 67, and ameasurement program 68, which perform actual processing of the operationand display unit 13, are stored in memory such as a hard disk.Hereafter, these will be described in detail.

The above-described plate layout program 66 creates a plate layout planof the tank bottom plate 31 by inputting basic data, required for thecreation of a tank plate cutting diagram, such as the number of theannular plates arranged around the tank bottom plate 31, and the size ofa plate which is a unit of the bottom plate 31 (refer to FIG. 7). Itbecomes possible to calculate the positional information of a plate bymaking this procedure (namely, a program) stored in a file, and todisplay only one plate on a CRT etc. independently. Here, the tank platelayout plan created is saved as plot data 70 in a file.

In addition, in the measurement program 68, the positional informationin a plate is added to the measured plate thickness data according tothe length, measured by the rotary encoder, in the measurement directionby inputting the distance and the measurement direction of the plate(unit plate), which is measured, from an origin by making an arbitrarycorner (or a specific position) of the bottom plate 31 be the origin.The data is saved by one point/channel at every fixed distance in themeasurement direction, i.e., one data per one subsection. When much dataexists in one subsection, a representative value (for example, a minimumplate thickness value) is saved as the data of the subsection. A plate,which is a measuring object, and a corner to be used as an origin areselected by using the plot data 70 created by the plate layout program66. In consideration of making the measuring cart 11 travel along theperiphery of the tank, it is possible to perform plate thicknessmeasurement even in the case of a circular travel of the measuring cart11 in addition to a straight travel. In addition, a file with thecreated information on the measuring points, plate thickness, and filmthickness is saved as measurement data 71.

Next, the plate thickness display program 67 will be described. Theplate thickness display program 67 creates a plate thicknessdistribution map for every plate and a whole plate thicknessdistribution map into which these are combined. Although these will bedescribed below, the creation of the plate thickness distribution mapper plate will be first described.

Color-coded display according to the concerned position-plate thicknessis performed for every plate by using the plot data 70 and themeasurement data 71. The following processing is performed so that aproper representative value of the measurement data 71 may be displayedon one pixel of a CRT (an example of a display) to display it. That is,as shown in FIG. 6, for example, one plate 72 is divided into a latticea side which is made to be an interval (a fixed interval in themeasurement direction) in which the measurement data 71 was acquired,and this one grid is made to be a cell 73. Next, a position and platethickness are calculated from the measurement data 71, and the platethickness data is set to the corresponding cell 73. Predeterminedoperation (for example, acquiring a minimum value) is performed whenplate thickness data has been already set to the cell 73 where to beset, and the plate thickness data of the cell 73 is updated. Here, thefile generated is saved as per-plate plate thickness data A in a file.Then, pixel size is calculated so that the whole plate may be displayedon the CRT. In addition, this pixel size is made to become an integralmultiple of the area of the cell 73. This number of cells gathered ismade to be a block 74 (in addition, the block 74 and a pixel have therelation of 1 to 1). A specific example is as follows.

EXAMPLE

When a number of CRT pixels is 640×480, a width of the plate is 7200 mm,and a cell size is 5 mm,

7200/640=11.25≧12 (mm/pixel), which is rounded up,

12/5=2.25≧3 (cells/pixel), which is rounded up,

and from the above, 3×3 cells are equivalent to one pixel.

Then, a representative value of the block 74 is calculated by performinga predetermined operation for the cells 73 every block 74 obtained bythe above method (for example, a minimum value is acquired), andcolor-coded display according to the plate thickness is performed to therepresentative value of this block 74. According to the above procedure,the proper color-coded distribution by the representative value can bedisplayed.

Next, the creation of a whole plate thickness distribution map will bedescribed.

The color-coded display according to the plate thickness is performedfor the whole tank bottom plate 31 by using the per-plate platethickness data A created with the above-described method. The followingprocessing is performed so that the proper representative value ofmeasurement data may be displayed in one pixel of the CRT for display.

First, the whole tank bottom plate 31 is divided into grids each side ofwhich is the integral multiple (for example, 5 times) of an interval (afixed interval in the measurement direction) in which measurement datais acquired. This one grid is called a cell H. Then, plate thicknessdata is set to the concerned cell H from the per-plate plate thicknessdata A. Predetermined operation (for example, acquiring a minimum value)is performed when plate thickness data has been already set to the cellH to be set, and the plate thickness data of the cell H is updated.Here, a file generated is called whole plate thickness data B.

Next, pixel size is calculated so that the whole tank bottom plate maybe displayed on the CRT (it is made to become the integral multiple ofthe cell H). This number of cells H gathered is called a block D. Theblock D and a pixel have the relation of 1 to 1, and a specific exampleis shown below.

EXAMPLE

When the number of CRT pixels is 640×480, the diameter of the tankbottom plate is 48000 mm, and a side of the cell is 25 mm,

48000/480=100 (mm/pixel), which is rounded up,

100/25=4 (cells/pixel), which is rounded up,

and from the above, 4×4 cells are equivalent to one pixel.

A representative value of the block D is calculated by performingpredetermined operation (for example, acquiring a minimum value) for thecells H every block D obtained by the above method, and color-codeddisplay according to the plate thickness is performed to therepresentative value of this block D. By these procedures, the propercolor-coded distribution according to the representative value can bedisplayed.

Next, a plate thickness measuring method for the bottom plate 31 of acylindrical tank where the plate thickness measuring apparatus 10 forthe bottom plate of a cylindrical tank according to an embodiment of thepresent invention is applied will be described.

Since the plate thickness measurement by the ultrasonic probes 22 and 23is performed by measuring time until a ultrasonic pulse emitted from atransmitting element is sent in order of a coating film, a steel plate,steel plate bottom reflection, the steel plate, and the coating film,and reaches a receiving element, the plate thickness measured by theultrasonic probes 22 and 23 are a combined thickness containing thetotal thickness of the coating film thickness and steel plate thickness.On the other hand, the thickness measured by the coating film thicknessgauges 24 and 25 is only coating film thickness. Therefore, steel platethickness, i.e., the thickness of the actual tank bottom plate 31 isobtained by subtracting the coating film thickness, measured by thecoating film thickness gauges 24 and 25, from the plate thicknessobtained by the ultrasonic probes 22 and 23, respectively withoutremoving the coating of the tank bottom plate 31.

In addition, the ultrasonic probes 22 and 23 and the coating filmthickness gauges 24 and 25 which are provided in six sets of auxiliarycarts 18 and 19 (one set is hidden in FIG. 3), arranged in the widthdirection, respectively are attached to the measuring cart 11 under thecertain positional relation in a plan view, and hence if what positionalrelation a certain position in the measuring cart 11 has with the tankbottom plate 31 is known, it is possible to know the positions of thetank bottom plate 31 that positions where the ultrasonic probes 22 and23 and the coating film thickness gauges 24 and 25 in the auxiliarycarts 18 and 19 perform measurement correspond to. Therefore, byattaching the rotary encoder 32, which measures traveling distance, tothe measuring cart 11, and grasping the traveling distance from aspecific position of the tank bottom plate 31, it is possible to specifyin real time the positions of the tank bottom plate 31 that positionswhere the ultrasonic probes 22 and 23 and the coating film thicknessgauges 24 and 25 that are moving perform measurement correspond to, andalso to measure the coating film thickness and the plate thickness ofthe specific position simultaneously. Thus, it is possible to obtain thesteel plate thickness at the specific position in the tank bottom plate31 by combining the plate thickness by the ultrasonic probes 22 and 23,the coating film thickness by the coating film thickness gauges 24 and25, and the measurement of the rotary encoder 32. In addition, if therelation between a position and steel plate thickness is displayed on ascreen, it is possible to determine plate thickness reduction by thecorrosion of the steel plate over the whole tank bottom plate 31.

In the actual plate thickness measurement of the tank bottom plate 31, ameasuring operator measures by manually moving the measuring cart 11along a path, determined beforehand, on the tank bottom plate 31. Thetraveling speed of the measuring cart 1 is determined in considerationof the processing speed of measurement data, and measurement is usuallyperformed at 500 to 1000 mm/second of traveling speed. In addition, inthis embodiment, although the measuring cart 11 is made to be ahandcart, it is also possible to make the measuring cart 11 be a mobilecart by providing a sensor if necessary, or determining a coursebeforehand.

Under a structure such as a base heater in a tank which has restrictionsin entrance height, by removing the handle 49 provided in the back cart16, the measuring cart 11 can enter, and it becomes possible to measurethe tank bottom plate 31.

In addition, since the controller 48 of the coating film thicknessgauges 24 and 25, and the display of measurements are incorporated inthe back cart 16, height H is, for example, 200 mm, but it is possibleto make the height of the front cart 15 be the height of about 100 mm.For this reason, it becomes possible to measure a gap of up to about 100mm by performing measurement only by the front cart 15 throughseparating or offsetting the front cart 15 from the measuring cart 11.At the time of measuring only by the front cart 15, it is possible toadopt a method of attaching a rope to the eyebolt 38 provided in thefront end of the front cart 15 and pulling the front cart 15.

If, on the tank bottom plate 31, an unmeasurable region arises near anobstruction such as a wear plate with the obstruction as a center owingto access limitation of the measuring cart 1, it becomes possible toreduce the unmeasurable region by separating or offsetting the frontcart 15.

In this embodiment, those that have the effective beam width of 25 mm,and the capacity of being able to detect a flat bottom hole with thediameter of 2 mm which exists in the range of 5 to 35 mm in themeasurement direction under a quiescent state are used as the ultrasonicprobes 22 and 23, eddy current type sensors which can measure thethickness range of 0 to 2 mm are used as the coating film thicknessgauges 24 and 25, and what can perform forward and backward distancemeasurement in the length measuring precision of 0.1% is used as therotary encoder 32. In this case, the measurement accuracy of platethickness at the time of combining the ultrasonic probes 22 and 23 withthe eddy current type sensors becomes ±0.1 mm.

Measurement data is recorded in the computer 64 (refer to FIG. 5) as arepresentative value, for example, in a 5-mm moving interval by findinga minimum value out of all the data read until the moving length becomes5 mm.

A pulse repetition frequency of the ultrasonic thickness gauge 63 is setto be 500 Hz to 2 kHz, and a range measured at the time of thetransmission and reception of ultrasonic pulses from the ultrasonicprobes 22 and 23 is made to be a range of 25 mm×3 mm (the value 25 mm iseffective beam width that is orthogonal to the moving direction of theultrasonic probes 22 and 23, and the value 3 mm is effective beam widthin the moving direction). Therefore, even if a measuring cart 11 ismoved at the rate of 500 to 1000 mm/sec, an incapable flaw detectionrange in the moving direction does not arise.

Therefore, in the plate thickness measuring apparatus for the bottomplate of a cylindrical tank according to an embodiment of the presentinvention, measurement will be performed at the following steps asdescribed above. First step (creation of tank bottom plate cuttingdiagram by plate layout program 66)

Based on the drawing of a tank, a bottom plate cutting diagram iscreated before the measurement.

Second Step (Measurement by Program 68)

A plate with which measurement is started is selected from the bottomplate cutting diagram.

Third Step (Selection of Origin of Measurement Starting Position)

The origin of a measurement starting position is selected from cornersof a plate.

Fourth Step (Input of Measurement Starting Position)

The measurement starting position is inputted in the distance from theorigin selected at the third step.

Fifth Step (Selection of Measurement Direction)

The measurement direction is selected from up, down, left, and rightdirections.

Sixth Step (Selection of Measurement Mode)

A straight line travel or a circular travel is selected.

Seventh Step (Start of Measurement)

The reference point of the measuring cart 11 is aligned with themeasurement starting position inputted at the fourth step, and themeasurement start switch 50 is pushed. Then, measurement is performed bypushing the measuring cart 11 in the measurement direction selected atthe fifth step.

Eighth Step (end of Measurement)

When a measuring cart holder comes to the end point of the plate in themeasurement direction, the measurement end switch 50 is pushed.

Ninth Step (Next Measurement)

The measuring cart 11 is moved to a next measurement starting position,and the fourth to eighth steps are repeated. Herewith, the measurementof the plate to be measured is completed.

Tenth Step (Creation of Per-plate Plate Thickness Distribution map)

The color-coded display of the plate to be measured with correspondingto the plate thickness is performed by using the plate thickness displayprogram 67.

Eleventh Step (Measurement of Next Plate)

The measurement of all the plates to be measured is completed byrepeating the second to tenth steps.

Twelfth Step (Creation of Whole Plate Thickness Distribution map)

The color-coded display of the whole tank bottom plate corresponding tothe plate thickness is performed by using the plate thickness displayprogram 67.

The plate thickness measuring apparatus 10 for the bottom plate of acylindrical tank according to an embodiment of the present inventionapplied to the plate thickness measurement of the bottom plate 31 of thecylindrical tank whose inside diameter is 15 m will be furtherdescribed. The contents of the measurement are divided into initialcondition setup, measurement condition setup, a measuring method, andmeasured result display.

Initial Condition Setup

A tank inside diameter, the number of annular plates, and the size of abasic bottom plate are inputted into the computer 64 of the operationand display unit 13.

Based on an input data, the computer 64 draws an annular plate, andcreates bottom plate cutting diagrams by dividing the whole bottom platevertically or horizontally, and further dividing each of the dividedregions. The divided regions are automatically numbered. FIG. 7 showsthe bottom plate cutting diagram created when the plate thicknessmeasurement is performed for the bottom plate 31 of a cylindrical tankwith an inside diameter of 15 m. Since such processing is describedabove in detail, it will be omitted here.

Measurement Condition Setup

The number of the plate (refer to FIG. 7), which is measured, isselected from the bottom plate cutting diagram, and the origin,measurement starting point, and measurement direction at the time ofmeasurement are determined about the plate having the selected number.

Measuring Method

a) The position of a measurement starting point is inputted in thedisplacement from the origin.

b) The reference point of the measuring cart 11 is aligned with themeasurement starting position, and the measurement start switch 50 ispressed.

c) The measuring cart 11 is moved in the measurement direction at thespeed of 500 to 1000 mm/second. The measuring cart 11 is moved so thatthe traveling direction of the measuring cart 11 may coincide with theoptical axis of a laser beam of a laser oscillator installed beforehandso that the measurement direction might be shown.

d) A measurement end switch 50 is pressed when the measuring cart 11arrives at the end point of the plate.

e) From the end point position, the measuring cart 11 is moved to a nextmeasurement starting position. In addition, when movement is in thedirection that is orthogonal (90°) to the measurement direction of themeasuring cart 11, a cross-directionally moving cart is used. Across-directionally moving cart is a dedicated cart for moving themeasuring cart 11 in the direction orthogonal to the measurementdirection of the measuring cart 11 with the measuring cart 11 beingplaced thereon.

f) When the measuring cart 11 moves on the whole surface in the platewith the selected number by repeating the above steps a) to e), themeasurement of the plate with the selected number is completed.

g) The number of the plate, which is measured next, is selected from thebottom plate cutting diagram, and steps a) to f) are performed.

h) When the plate thickness measurement of all the plates in the bottomplate cutting diagram is completed, it means that the plate thicknessmeasurement of the tank bottom plate 31 is completed.

Measured Result Display

During the measurement, the measured results of the plate thickness ofthe bottom plate (steel plate) 31 can be displayed in color-codingaccording to the grade of plate thickness in real time, and platethickness reduction can be shown on a screen. After the measurement, themeasured results of steel plate thickness can be displayed into thebottom plate cutting diagram in color-coding according to the grade ofplate thickness, and the color-coded plate thickness distribution map, astate of plate thickness cross sections in the vertical and horizontaldirections at an arbitrary position, or the like can be displayed on ascreen by selecting a plate with an arbitrary number. These contentsdisplayed on a screen can be outputted by a color printer that is anexample of an output unit. In addition, it is possible to display andoutput an average of plate thickness, a minimum value of platethickness, and the distribution of areas of portions, whose platethickness is more than a fixed plate thickness, according to the numberof a plate. The distribution situation of positions with a bottom platethickness of less than 8 mm against the design bottom plate thickness of10 mm is shown in FIG. 8 as an example of plate thickness reductionobtained in the plate thickness measurement of the bottom plate 31 of acylindrical tank with an inside diameter of 15 m. In addition, therelation of the bottom plate thickness and area that is obtained overthe whole tank bottom plate 31 is shown in Table 1. Since suchprocessing is described above in detail, it will be omitted here.

TABLE 1 Class of steel plate thickness (mm) Area (cm²) Rate (%) Note t ≧10 845678 44.5  10 > t ≧ 9.0 1031905 54.3 9.0 > t ≧ 8.0 2260 0.1 8.0 > t≧ 7.0 25 0.0 t < 7.0 0 0.0 Not measured 21080 1.1 Unmeasurable areaTotal 1900948 100.0 Design steel plate thickness: 10.0 mm Average steelplate thickness: 9.83 mm Minimum steel plate thickness: 7.10 mm

Moreover, although specific numbers are used for description in theabove-described embodiment, the present invention is not limited tothese numbers.

Industrial Applicability

In a plate thickness measuring apparatus for the bottom plate of acylindrical tank according to the present invention, a measuring cart ismoved, in which reflection type ultrasonic probes which measure thethickness of a tank bottom plate, coating film thickness gauges whichmeasure coating film thickness on the surface of the bottom plate, and arotary encoder which measures traveling distance are attached, on thetank bottom plate, to measure the thickness of the actual bottom plateat a specific position of a tank bottom surface, and to display therelation between the position and the thickness in real time on ascreen. Hence it becomes possible to accurately, simply, and quicklymeasure and evaluate plate thickness reduction by the corrosion of alocal steel plate over the whole tank bottom plate without removing thecoating of the tank bottom plate. Since it becomes possible to performmeasurement by setting the traveling speed of a measuring cart to be 500to 1000 mm/second, it becomes possible to perform high-speed platethickness measurement.

In a plate thickness measuring apparatus for the bottom plate of acylindrical tank according to the present invention, if auxiliary cartsare arranged in a plurality of rows in the traveling direction of ameasuring cart, and furthermore, in a staggered or step-like pattern, itis possible to perform a wide range of plate thickness measurementsimultaneously, and to attain easy and rapid measurement.

In addition, in a plate thickness measuring apparatus for the bottomplate of a cylindrical tank according to the present invention, since adouble crystal probe of a transmitting element and a receiving elementis composed of a reflection type ultrasonic probe, and an eddy currenttype sensor is composed of a coating film thickness gauge, it ispossible to accurately measure and evaluate plate thickness reductionwithout removing the coating of a tank bottom plate.

In a plate thickness measuring apparatus for the bottom plate of acylindrical tank according to the present invention, since the height ofthe whole measuring cart is made to be able to measure the thickness ofa tank bottom plate while passing under the piping provided above thetank bottom plate, a large area of the tank bottom plate can bemeasured.

What is claimed is:
 1. A plate thickness measuring apparatus for abottom plate of a cylindrical tank characterized by comprising: ameasuring cart which travels on a tank bottom plate to be measured;plural auxiliary carts which are arranged in a width direction of themeasuring cart and moreover attached to the measuring cart throughuniversal joint mechanisms; reflection type ultrasonic probes whichmeasure a thickness of the tank bottom plate, and coating film thicknessgauges which measure a thickness of a coating film on a surface of thetank bottom plate, both of which are attached in each of the auxiliarycarts; a rotary encoder which is attached to the measuring cart andmeasures a traveling distance of the measuring cart; and an operationand display unit which inputs outputs of the respective ultrasonicprobes, outputs of the respective coating film thickness gauges and anoutput of the rotary encoder, measures and stores an actual thickness ofthe tank bottom plate that is obtained by subtracting the thickness ofthe coating film at a specific position of the tank bottom plate basedon the output of the respective ultrasonic probes and the output of therespective coating film thickness gauges, furthermore, specifies theposition by the rotary encoder and displays the relation between theposition of the bottom plate and the thickness thereof on a screen bycolor-coding according to the measured thickness of the tank bottomplate, wherein the respective auxiliary carts are arranged in pluralrows in the traveling direction of the measuring cart, and the auxiliarycarts are arranged in a staggered or step-like pattern in a plan view,whereby the adjacent ultrasonic probes are prevented from interferingeach other and measurement of a whole region of the width direction ofthe measuring cart is possible by the ultrasonic probes attached to theauxiliary carts, and moreover, the coating film thickness gauges beingprovided separately from the ultrasonic probes, furthermore, the eachultrasonic probe being comprised of a double crystal probe in which atransmitting element and a receiving element are separated.
 2. The platethickness measuring apparatus for a bottom plate of a cylindrical tankaccording to claim 1, characterized in that the measuring cart comprisesa front cart and a back cart which are arranged and connected front andback, the plural auxiliary carts in two rows arranged front and back arearranged in a staggered pattern in a plan view in an opening formed in alower middle of the front cart, and furthermore, a horizontal guidewheel is provided respectively in a front and a back of an upper portionof the front cart through a supporting table.
 3. The plate thicknessmeasuring apparatus for a bottom plate of a cylindrical tank accordingto claim 2, characterized in that the ultrasonic probes are provided ina middle portion of the respective auxiliary carts and the coating filmthickness gauges are provided in a front portion or a back portion ofthe respective auxiliary carts.
 4. The plate thickness measuringapparatus for a bottom plate of a cylindrical tank according to claim 1,characterized in that an operation handle provided in the measuring cartis detachable, whereby it is possible to measure the thickness of thetank bottom plate by the measuring cart passing under piping providedabove the tank bottom plate.
 5. The plate thickness measuring apparatusfor a bottom plate of a cylindrical tank according to claim 1,characterized in that an ultrasonic thickness gauge is provided suchthat a pulse repetition frequency added to the respective ultrasonicprobes is 500 Hz to 2 kHz.
 6. The plate thickness measuring apparatusfor a bottom plate of a cylindrical tank according to claim 1,characterized in that an ultrasonic thickness gauge is provided suchthat a pulse repetition frequency added to the respective ultrasonicprobes is smaller than a value which an effective beam width of atraveling direction of the ultrasonic probe is divided by a travelingspeed of the measuring cart, whereby plate thickness measurement ispossible for all traveling directions of the measuring cart.